This invention relates to a method for forming cutting elements and specifically to a method for forming cutting( elements having a non-uniform interface adjacent their cutting layers.
Cutting elements, such as shear cutters for rock bits, for example, typically have a body (or substrate) which has a cutting face. A cutting layer (sometimes referred to as a "cutting table") is bonded to the cutting face of the body. The body is generally made from cemented tungsten carbide (sometimes referred to simply as "tungsten carbide" or "carbide"), while the cutting layer is made from a polycrystalline ultra hard material, such as polycrystalline diamond ("PCD") or polycrystalline cubic boron nitride ("PCBN"). Moreover, these cutters may employ transition layers bonded between the substrate and the cutting layer. The transition layers typically have properties which are intermediate between the properties of the substrate and the cutting layer.
To reduce the residual stresses formed on the interface between the substrate and the cutting layer and to enhance the delamination resistance of the cutting layer, irregularities are sometimes incorporated on the cutting face of the substrate, forming a non-uniform interface between the substrate and the cutting layer. When transition layers are incorporated, one or both faces of the transition layers may also be non-uniform.
As used herein, a uniform interface is one that is flat or always curves in the same direction. This can be stated differently as an interface having the first derivative of slope always having the same sign. Thus, for example, a conventional polycrystalline diamond-coated convex insert for a rock bit has a uniform interface since the center of curvature of all portions of the interface is in or through the carbide substrate.
On the other hand, a non-uniform interface is defined as one where the first derivative of slope has changing signal. An example of a non-uniform interface is one that is wavy with alternating peaks and valleys. Other non-uniform interfaces may have dimples, bumps, ridges (straight or curved) or grooves, or other patterns of raised and lowered regions in relief.
There are a few methods currently being used for forming a non-uniform interface between the substrate and the cutting layer, or between a transition layer and the substrate, or between the a transition layer and the cutting layer. One method requires presintering the substrate. Grooves or other irregularities are then milled or EDM-sunk into the cutting face of the presintered substrate. If a transition layer is to be incorporated, the transition layer may be laid in powder form over the grooved cutting face of the substrate. The ultra hard material layer is then laid over the transition layer. The ultra hard material is also typically laid in powder form.
In situations where a non-uniform interface is required between the transition layer and the ultra hard material layer grooves or other irregularities may be pressed on top of the powder transition layer during a presintering process. The ultra hard material is then applied over the presintered transition layer and the entire assembly consisting of the substrate, transition layer and ultra hard material is sintered in a conventional high temperature, high pressure process.
Other methods of forming non-uniform interfaces commonly require that the grooves are formed on the substrate cutting face during the substrate presintering process. Typically the substrate is formed from a powder tungsten carbide material. Grooves are pressed on a portion of the powder substrate that would form the cutting face while the substrate is being presintered.
As can be seen, the methods currently used for forming a cutting element having non-uniform interfaces between the cutting layer and the substrate, or between the cutting layer and a transition layer, or between the substrate and a transition layer may be labor intensive. As such, there is a need for a simpler method of forming a cutting element having a non-uniform interface.